Microdecompression for Lumbar Spinal Canal Stenosis

Transcription

1 Microdecompression for Lumbar Spinal Canal Stenosis SPINE Volume 24, Number 21, pp , Lippincott Williams & Wilkins, Inc. Bradley K. Weiner, MD, Matthew Walker, MD, Richard S. Brower, MD, and John A. McCulloch, MD FRCS(C) Study Design. A description of the technique for lumbar microdecompression and a prospective study of the outcomes. Objective. To describe and analyze a technique that affords an excellent decompression while minimizing damage to surrounding tissues. Summary of Background Data. Commonly used techniques of lumbar decompression that include bilateral takedown of paraspinal musculature and aggressive bony resection can result in significant iatrogenic sequelae. A less destructive alternative is needed. Methods. Unilateral limited takedown of multifidus was undertaken, and ipsilateral decompression performed. The contralateral side then was addressed under the midline structures with microscopic visualization thereby preserving the supra-/interspinous ligament complex and the contralateral musculature. Thirty consecutive patients undergoing the procedure were analyzed prospectively and after a follow-up period by independent observers using a modified validated functional outcome score and patient satisfaction measures. Results. The technique affords an excellent decompression while minimizing destruction to tissues not directly involved in the pathologic process. Functional outcome scores doubled, and 87% of patients reported high satisfaction rates. Conclusions. Lumbar microdecompression is a minimally invasive technique that appears to provide excellent functional outcomes. [Key words: laminectomy, lumbar spine, microdecompression, spinal canal stenosis] Spine 1999;24: From the Spinal Unit, Department of Orthopaedic Surgery, Summa Health Systems and Northeastern Ohio Universities, College of Medicine, Akron, Ohio. Acknowledgment date: October 2, First revision date: January 27, Acceptance date: March 8, Device status category: 1. The surgical management of lumbar degenerative spinal canal stenosis has become progressively less invasive. Older techniques of laminectomy or unroofing of the spinal canal, while affording wide decompression, often resulted in destruction or insufficiency of the pars interarticularis or facet joints with resultant iatrogenic instability. Increasing knowledge of the pathoanatomy, coupled with the development of magnetic resonance imaging, has allowed a more precise delineation of soft tissue and bony stenosing lesions. In the degenerative setting, it has been noted that the majority of neurologic compression occurs at the level of the interlaminar window. Accordingly, this window has been used to afford adequate decompression by laminotomy, excision of ligamentum flavum, and trumpeted undercutting techniques of partial facetectomy, while residual lamina, pars, and facet are maintained. Despite these advances, significant destruction of tissues uninvolved in the pathologic process persist. Multifidus is elevated from spinous processes and laminae bilaterally and then retracted widely. The supraspinous and interspinous ligaments are resected along with their bony attachments to the spinous processes. These iatrogenic insults may have important consequences. The paraspinal muscles may be denervated, 9 and subsequent atrophy 10 may occur changes that have been correlated with the postoperative failed back syndrome. 10 Stability in flexion is altered with loss of the supra-/ interspinous ligament complex. 3 Dead space is increased, which may increase local wound complication rates (such as infection), as well as expand the volume to be filled in by scar potentially necessitating as well as complicating revision surgical procedures. Additionally, the posterior median furrow is lost and may be of cosmetic concern to the patient. Initially described by Young et al in and subsequently modified by McCulloch, 7 a microscopic technique characterized by unilateral multifidus retraction, ipsilateral microdecompression, and contralateral microdecompression performed under the midline posterior structures has been used at the current authors center since In this report, the authors 1) describe the technique, 2) prospectively evaluate the outcomes of the technique, and 3) discuss its advantages while addressing concerns regarding its use. Materials and Methods Operative Technique. Anesthesia and Positioning. General endotracheal anesthesia is used in all cases, and the patient is placed on the spinal frame with gentle lumbar flexion to afford widening of the interlaminar spaces. Superficial Exposure. Preoperative image intensification is used to localize the involved segment. The incision is midline and extends over, but is limited to, the underlying region of stenosis as documented on magnetic resonance imaging. A curvilinear paramedian fascial incision then is made on the patient s most symptomatic side, approximately 1 cm off midline. Using a Cobb elevator, multifidus is elevated gently off the laminae at the involved segments and is retracted to the medial border of the facet joint. A self-retaining microdiscectomy retractor then is used. A full view of the ipsilateral interlaminar space is now afforded, and the microscope is brought into place. Interlaminar Exposure. Using Kerrison rongeurs or a highspeed burr, an ipsilateral laminotomy of the cephalad hemi- 2268

2 Microdecompression for Lumbar Spinal Canal Stenosis Weiner et al 2269 lamina is performed. It is extended cephalad until the insertion of the ligamentum flavum is reached. This may be performed in a trumpeted fashion to allow maximal laminar preservation, angling the microscope upward. A similar but less extensive laminotomy then is performed on the ipsilateral caudal lamina, which allows removal of the intervening ligamentum flavum and affords a midline hemidecompression. The microscope then is angulated into the ipsilateral subarticular zone and, moving cephalad to caudal, soft tissue and bony stenosing pathology is excised using Kerrison rongeurs. This is done sequentially and throughout the interlaminar window until the cephalad and caudal nerve roots at the operative level are seen exiting freely into the foramen. This should be performed in a trumpeted fashion to maximally preserve the pars interarticularis and facet joint. After complete ipsilateral microdecompression, the contralateral side is addressed. The microscope is angulated medially and, quite often, the patient tilted contralaterally, to afford visualization across the midline beneath the deepest portion of the interspinous ligament. This deepest portion is excised to allow the posterior surface of the contralateral ligamentum flavum to be seen. A probe is used to confirm that the anterior surface of the ligamentum is free from adhesion to the dura, and the ligamentum then is resected sequentially from cephalad to caudal and medial to lateral (Figures 1 and 2). This affords, by nature of the scope angulation, a trumpeted decompression, which is extended lengthwise and laterally in a fashion similar to that described for the ipsilateral microdecompression. A vital step in the process, to allow access for contralateral hemilaminotomies, is the adequate resection of the wishbone portions of the cephalad and caudal lamina, i.e., the junction of lamina with spinous process. After decompression, the spinal canal should have been sculptured to normal sagittal and transverse diameters, and all soft tissue and bony stenosing pathology should have been resected (Figure 3). Structures not directly involved in the pathologic condition should be preserved. Closure. The wound is irrigated, and hemostasis obtained. Whether to use a deep drain is at the discretion of the surgeon, as is whether to use a barrier substance (fat graft). The fascia, subcutaneous tissue, and skin then are closed sequentially in a standard fashion. Patients. Thirty consecutive patients who were scheduled to undergo the described lumbar decompression (October 1996 March 1997) for neurogenic claudication secondary to degenerative spinal canal stenosis confirmed by magnetic resonance imaging and who had undergone failed conservative measures were studied. No patients had concomitant disc herniations or instability, e.g., degenerative spondylolisthesis, and, accordingly, none underwent discectomy or fusion. All patients were operated on by a single surgeon (J.A.M.) using the described technique. Inclusion criteria are noted in Table 1. Figure 1. Microdecompression. The shaded area demonstrates the ipsilateral decompression. The hashed lines demonstrate the contralateral area to be addressed under the midline structures; visualization is afforded by angulation of the microscope toward the contralateral interlaminar window. Data. Prospective data included basic demographics and the Neurogenic Claudication Outcome Score (NCOS). Operative data included the number of levels decompressed and any complications. Follow-up data included the NCOS and two patient satisfaction measures. The NCOS is a simple, concise, self-administered outcome questionnaire. It is based on and represents an expansion of the Low Back Outcome Score developed by Fraser s group in Adelaide, 4 specifically tailored to address patients with neurogenic Figure 2. Axial view of the contralateral decompression. Care should be taken to protect the contralateral exiting nerve root.

3 2270 Spine Volume 24 Number Figure 3. Axial view of spinal segment, postdecompression. claudication. The questionnaire and the manner by which it is scored are shown in Table 2. The additional follow-up patient satisfaction questions are shown in Table 3. All preoperative and postoperative questionnaires were administered, collected, and evaluated by independent observers (B.K.W., M.A.W.). A 9-month follow-up period was chosen, as opposed to the standard 2 years, to avoid possible subsequent degeneration in this patient population as per the recommendation of Stucki et al 11 regarding the evaluation of outcomes in patients with spinal canal stenosis. Additionally, test retest was performed after surgery on 10 randomly selected patients 2 weeks after their 9-month postoperative assessment. Data collected were nonparametrically distributed and ordinal. Thus, the Wilcoxon s rank sum test was used to confirm statistical significance. Results Of the 30 patients included in the study, 16 were women, and 14 were men. The average age was 68 years, with a range from 41 to 81 years. The average preoperative NCOS was 32 of a possible 100, with a range from 2 to 70. The duration of the patients symptoms before surgery averaged 2 years, with a range from 3 months to 8 years. Nine patients had one level decompressed, 14 had two levels, 4 had three levels, 2 had four levels, and 1 had five levels. There were no intraoperative complications. Four patients had postoperative serous drainage requiring sequential dressing changes. One of these patients was culture-positive for Staphylococcus aureus, which was sensitive to and managed successfully with oral antibiotics. No patients were lost to follow-up. The average follow-up NCOS was 67 of 100, with a range from 29 to 100. This was highly statistically significant using the Wilcoxon s rank sum test. Thirteen patients were very satisfied with their outcome, 13 were fairly satisfied, 3 were not very satisfied, and 1 patient believed he was worse and was very dissatisfied. Twenty-nine of the 30 patients would recommend the procedure to a friend with the same problem. Ten randomly selected patients had test retest of their follow-up results. The average initial follow-up NCOS was 64, and the average retest NCOS was 68, demonstrating consistency in responses. The results are summarized in Table Four. Responses to specific questions within the NCOS revealed quite consistent findings regarding patient outcomes as follows: 1. After surgery, the average patient s ability to walk distances increased from approximately 100 yards to between a half and a full mile. 2. After surgery, average standing time increased from 10 minutes to a half hour. 3. Back pain and leg pain, numbness, and heaviness each decreased from moderate to mild. 4. Interference with daily activities decreased from moderate to mild. 5. Once symptoms arose, the time to resolution after sitting was unchanged after surgery, remaining between 5 and 10 minutes. 6. Pain medication use was decreased from daily to occasionally. 7. Consultations with physicians decreased from monthly to rarely. Discussion The described approach to lumbar decompressive surgery has several advantages: Paraspinal Musculature Commonly used techniques of exposure for lumbar decompression that include elevation of the multifidus bilaterally with subsequent wide retraction have potentially serious consequences. Mayer et al 6 demonstrated a decrease in paraspinal muscle strength with concomitant atrophy on postoperative computed tomography scans. See and Kraft 9 found long-term alterations in electromyographic evaluation up to 4 years after surgery. Sihvonen et al 10 noted similar computed tomography and electromyographic abnormalities and correlated these with the postoperative failed back syndrome. Innervation of the multifidi derives from the medial branch of the dorsal ramus. After the dorsal ramus splits Table 1. Inclusion Criteria 1. Symptoms of neurogenic claudication referable to the lumbar spine (claudicant or radicular symptoms brought on by walking or prolonged standing, relieved by sitting or the flexed position, in the absence of vascular or neuropathic pathology) 2. Failure of conservative measures; minimum 3 months 3. MRI demonstrating neurologic compression by hypertrophied (infolded) ligamentum flavum, osteophytic facet joints, and annular bulging 4. Absence of associated pathology congenital stenosis, disc herniations, or spondylolisthesis

4 Microdecompression for Lumbar Spinal Canal Stenosis Weiner et al 2271 Table 2. Neurogenic Claudication Outcome Score and How to Calculate It 1. How far can you walk before having to stop and rest? a) 100 yards (0 points) b) Between 100 yards and 1 2 mile (2 points) c) Between 1 2 and 1 mile (4) d) Greater than 1 mile (6) 2. How long can you stand still before looking for a place to sit down? a) 5 min (0) b) 5 to 15 min (2) c) 15 to 45 min (4) d) as long as I want (6) 3. Once your symptoms arise, you have: None Mild Moderate Severe Back pain (6) (4) (2) (0) Leg pain (6) (4) (2) (0) Numbness/tingling (6) (4) (2) (0) Heaviness/weakness (6) (4) (2) (0) 4. How much do your symptoms affect the following activities? Not at All (can do easily) Mildly (symptoms, but can do) Moderately (difficult, but can do) Sports or activities (6) (4) (2) (0) Household or odd jobs (6) (4) (2) (0) Walking (6) (4) (2) (0) Standing (6) (4) (2) (0) Sitting (6) (4) (2) (0) Sex life (6) (4) (2) (0) 5. How long must you rest before the symptoms resolve? a) 5 min (6) b) between 5 and 10 min (3) c) 10 min (0) 6. How frequently do you take pain medicine for your back/leg pain? a) Never (6) b) Occasionally (4) c) Daily (2) d) Frequently (0) 7. How frequently do you see a doctor for your back/leg pain? a) Never (6) b) Rarely (4) c) Monthly (2) d) Frequently (0) 8. Please indicate the level of your pain on the following scale: (scored as 10 X) No pain Worst pain possible Note: Total points possible 100 (asymptomatic, full function). Severely (impossible to do) off, it pierces the intertransverse ligament and proceeds posteriorly to loop around the facet joint. At this point, it divides into medial, intermediate, and lateral rami, which innervate multifidus, longissimus, and iliocostalis, respectively. The medial branch courses around the superior articular process to lie in a groove between the mamillary process and the accessory process, where it may be covered by a fibro-osseous ligament. It then innervates the multifidus in a segmental fashion with no overlap. 1,2 Retraction of multifidus beyond the midpoint of the facet joint tethers the medial branch within the mamilloaccessory groove, risking muscular denervation. The described technique of microdecompression limits ipsilateral retraction to the level of the medial facet border. Contralaterally, no elevation or retraction of the paraspinal musculature is undertaken, thereby minimizing the risk of iatrogenic muscular trauma. Table 3. Satisfaction Measures 1. Overall, how successful has your operation been? a) Very successful, almost complete relief b) Fairly successful, a good deal of relief c) Not very successful, only a little relief d) Failure, no relief e) Worse than before 2. If you had a friend with the same trouble you had, would you recommend the operation to your friend? Yes/No Inter-/Supraspinous Ligaments Most surgical approaches to decompression involve excision of the interspinous or supraspinous ligament complexes, altering an already pathologic biomechanical milieu. Goel et al 3 found that, under normal conditions, the supraspinous ligament experienced the greatest force when exposed to an external flexion moment across an anatomic segment. Hindle et al 5 also demonstrated load with flexion in the supra- and interspinous ligaments. Prestar 8 observed similar findings and believed that, in regions lacking this ligamentous support, the paraspinal musculature must come to the aid of stability. Unfortunately, the pathologic setting of severe degenerative disease may increase the demands placed on these posterior ligaments. Loss of lordosis, disc degeneration with segmental instability, altered facet joint biomechanics, laxity of the facet joint capsules, and postoperative insufficiency of the paraspinal musculature each can increase the role played by this posterior ligamentous complex. Accordingly, it seems clear that every effort should Table 4. Summary of Results No. of patients: 30 Males: 16 Females: 14 Duration of symptoms prior to surgery: 2 yr (range 3 mo 8 yr) Average age: 68 yr (range yr) Neurogenic Claudication Outcome Score Preoperative: avg 32 (range 2 70) Postoperative: avg 67 (range ) Test/retest Postoperative I: Average 64 Postoperative II: Average 68 Satisfaction measures Very 13 Fairly 13 Not very 3 Dissatisfied 1 29 of 30 would recommend to a friend with same symptoms

5 2272 Spine Volume 24 Number be made to preserve this complex in this setting, and the described technique of microdecompression achieves this goal well. Dead Space Postsurgical dead space has serious potential consequences. Increased volume to be filled results in increased blood loss and provides an ideal bacterial culture medium with potential for increasing the infection rate. The region is inevitably replaced with scar tissue, thereby complicating or necessitating secondary surgical interventions. Resection of portions or all of the spinous processes, interspinous ligaments, and supraspinous ligaments, and iatrogenic damage to the paraspinal musculature results in a large volume of dead space. Dead space and its consequent risks are significantly decreased using the described technique. Cosmesis The cosmetic goals of surgery are simple: limit the incision length and maintain the region s normal appearance. The microdecompression approach allows the incision to be limited to the immediate region of decompression. Additionally, maintenance of the spinous processes and inter-/supraspinous ligamentous complex (with its posterior lumbar fascial attachment) maintains the normal posterior median furrow often lost using other more destructive techniques. Decompression The recent rise in minimally invasive operative techniques has been based on the rather honorable goals of minimization of destruction to nonpathologic tissues and optimization of the cosmetic result. The rather limited adoption and often short lifespan of many of these techniques demonstrate the most basic honorable surgical goal get the job done completely and safely. The use of the described microdecompression appears to satisfy this goals rather well. Concerns Given the above advantages, several questions of concern may arise regarding the described technique of microdecompression: Is it Technically Demanding? Without question, this is the greatest concern. Working through the small operative window at a significant angle to address the contralateral side requires an extensive knowledge of lumbar microanatomy and considerable experience with both Kerrison and microscope, i.e., this is not a case for the chief resident or the occasional spine surgeon. What about Laminectomies? Cases of severe stenosis with multilevel involvement and crowding of the interlaminar window or cases of congenital stenosis quite often result in the need to perform complete laminectomies. In general, these groups are found to comprise approximately 10% of patients with stenosis who are treated with surgery. Obviously, this technique cannot be applied in this patient population. Conclusions The described microdecompression minimizes resection of and injury to tissues not directly involved in the pathologic process, while affording a safe and thorough decompression. The outcomes appear quite satisfactory with significant pain relief, improvement in function, and patient satisfaction noted in the great majority of cases. References 1. Bogduk N. The lumbar mamilloaccessory ligament: Its anatomical and neurosurgical significance. Spine 1981;6: Bogduk N, Wilson AS, Tynan W. The human lumbar dorsal rami. J Anat 1982;134: Goel VK, Fromknecht SJ, Nishiyama K, Weinstein J, Liu YK. The role of the lumbar spinal elements in flexion. Spine 1985;10: Greenough C, Fraser RD. Assessment of outcome in patients with low back pain. Spine 1992;17: Hindle RJ, Pearcy MJ, Cross A. Mechanical function of the human lumbar interspinous and supraspinous ligaments. J Biomed Eng 1990;12: Mayer TG, Vanharanta H, Gatchel RJ, et al. Comparison of CT scan muscle measurements and isokinetic trunk strength in postoperative patients. Spine 1989;14: McCulloch JA. Microsurgical Spinal Laminotomies in The Adult Spine: Principles and Practice. J.W. Frymoyer, ed. New York: Raven Press, Ltd., Prestar FJ. Morphology and function of the interspinal ligaments and the supraspinal ligament of the lumbar portion of the spine. Morphol Med 1982;2: See DH, Kraft GH. Electromyography in paraspinal muscles following surgery for root compression. Arch Phys Med Rehabil 1975;56: Sihvonen T, Herno A, Paljarva L, Airaksinen O, Patanen J, Tapaninaho A. Local denervation atrophy of paraspinal muscles in postoperative failed back syndrome. Spine 1993;18: Stucki G, Daltroy L, Liang, et al. Meaurement properties of a selfadministered outcome measure in lumbar spinal stenosis. Spine 1996;21: Young S, Veerapen R, O Laoire SA. Relief of lumbar canal stenosis using multilevel subarticular fenestrations as an alternative to wide laminectomy. Neurosurgery 1988;23: Address reprint requests to Bradley K. Weiner, MD Summit Orthopaedic Group 20 Olive Street, Ste. 200 St. Thomas Hospital Akron, Ohio 44310